[WordPress] Find posts that are not tagged with at least one tag in a range of tags.

query-untagged-posts.php

<?php

add_action( 'admin_init', 'acme_query_for_untagged_posts' );
/**
 * Query for all public posts that are not tagged with at least
 * one term from a set of term IDs.
 */
function acme_query_for_untagged_posts() {

	$args = array(
		'post_type'      => 'post',
		'post_status'    => 'public',
		'posts_per_page' => -1,
		'tax_query'      =>  array(
					array(
						'taxonomy' => 'my_custom_tax',
						'field'    => 'term_id',
						'terms'    => array( 10, 15, 20, 25, 30 ),
						'operator' => 'NOT IN'
					)
				)

	);
	$acme_query = new WP_Query( $args );
	
	/* At this point, you can return the result, iterate through
	 * the query and update the posts, etc.
	 */

}

tag-untagged-cpts.php

<?php

/* This gist assumes that the query in
 * https://gist.github.com/tommcfarlin/6537bcaf6ac77e3bbfeb#file-query-untagged-posts-php
 * returns the instance of $acme_query that's defined in the function.
 *
 * Also note that this is contingent upon acme_query_for_untagged_posts() passing
 * post_type => 'my_cpt' rather than 'post'.
 */

$acme_query = acme_query_for_untagged_posts();

/* Define an array of integers each of which corresponds to a tag that needs
 * to be added to each post. In this case, it's only adding the term that
 * has the ID of 2.
 */
$term_ids = array( 2 );

if ( $acme_query->have_posts() ) {

	while ( $acme_query->have_posts() ) {
		
		$acme_query->the_post();
		wp_set_object_terms( get_the_ID(), $term_ids, ‘my_custom_tax’, TRUE );
		
	}

}

tag-untagged-posts.php

<?php

/* This gist assumes that the query in
 * https://gist.github.com/tommcfarlin/6537bcaf6ac77e3bbfeb#file-query-untagged-posts-php
 * returns the instance of $acme_query that's defined in the function.
 */

$acme_query = acme_query_for_untagged_posts();

/* Define an array of integers each of which corresponds to a tag that needs
 * to be added to each post. In this case, it's only adding the term that
 * has the ID of 2.
 */
$term_ids = array( 2 );

if ( $acme_query->have_posts() ) {

	while ( $acme_query->have_posts() ) {
		
		$acme_query->the_post();
		wp_set_post_terms( get_the_ID(), $term_ids, ‘my_custom_tax’ );
		
	}

}